1. Field of the Invention
The present invention relates to a charged beam apparatus for performing deposition or etching of a thin film by using a charged beam such as an ion beam and a gas.
2. Description of the Related Art
A charged beam apparatus, e.g., a focused ion beam (FIB) apparatus is capable of fine processing for samples and therefore used in correcting defects on the surface of a mask or of a large scale integrated (LSI) circuit.
The methods by which this correction is done include, in addition to sputter etching, a processing method (FIB assisted etching) in which etching is performed by irradiating an FIB while a gas is supplied onto a sample, and a processing method (FIB assisted deposition) in which deposition is performed in the same fashion. In these methods the focused ion beam apparatus is equipped with a gas supply mechanism for supplying a gas onto a sample. A nozzle type mechanism and a cylinder type mechanism are examples of the gas supply mechanism.
FIG. 1 shows an example of the arrangement of a focused ion beam apparatus having a nozzle type gas supply mechanism. As in FIG. 1, this focused ion beam apparatus includes a column 41, and an ion beam is emitted downward from an ion source 42 accommodated in the column 41.
This focused ion beam apparatus also has a chamber 46 which includes a charge neutralizer 44 and a secondary charged particle detector 45. In this chamber 46 a sample 48 is placed on a stage 47. The ion beam emitted from the ion source 42 is irradiated on a predetermined position (to be processed) of the sample 48. A nozzle having a gas supply opening 49 is provided in the chamber 46. This nozzle can be horizontally moved by a driving mechanism 50 so that a gas from the gas supply opening is injected toward the processing position.
The secondary charged particle detector 45 detects secondary charged particles (secondary ions or secondary electrons) generated during FIB assisted deposition or FIB assisted etching. The detector 45 is used to obtain an SIM (Scanning Ion Microscopy) image for searching for the position to be processed on the sample 48. The position to be processed is set on the basis of this SIM image. Before the gas is supplied, the nozzle is moved up away from the sample in order that the shadow of the nozzle have no influence on the SIM image. The nozzle is moved down close to the sample during gas supply.
In the focused ion beam apparatus having the nozzle type gas supply mechanism, two or more nozzles must be provided if it is necessary to supply two or more types of gases from different nozzles. In this case it becomes difficult to arrange these nozzles and a driving mechanism for moving these nozzles becomes complicated.
A disk-like detector called an MCP (MultiChannel Plate) is also available as the secondary charged particle detector in addition to the rod-like detector described above. As illustrated in FIG. 2, an MCP 51 is so arranged as to close the end portion of the column 41. A hole for passing the ion beam is formed in a central portion of the MCP 51.
Unfortunately, combining the nozzle type gas supply mechanism and the MCP as in FIG. 2 raises the following problem. That is, when the nozzle is present near the surface of the sample 48, due to the effect of the nozzle the potential distribution is no longer symmetrical about the axis of the ion beam. Consequently, the shadow of the nozzle appears in the SIM image of the sample 48 obtained when the MCP 51 detects secondary charged particles. This makes an accurate setting of the processing position impossible.
The cylinder type gas supply mechanism has no such problem as the nozzle type mechanism. That is, by the use of a cylinder type gas supply mechanism 52 having a funnel-like upper portion, FIG. 3, it is possible to obtain an almost symmetrical potential distribution between the sample 48 and the MCP, since there is no projecting portion which interferes with secondary particles produced by the sample 48 before they reach the MCP. As a result, no extra shadow appears in the SIM image of the sample 48, and the processing position can be accurately set accordingly. Also, a simple arrangement is possible even when two or more gas supply openings are used.
The lower portion of the cylinder type gas supply mechanism is formed as shown in FIG. 4A (a section viewed from the above). A hole 54 is formed in the center of the gas supply mechanism, and, for example, two gas supply pipes 55a and 55b are disposed to extend from the outside to the center of the inside. A focused ion beam is so set as to be incident on the sample surface (the position indicated by a point P) through the center of the hole 54. Gas supply openings 56a and 56b of the gas supply pipes 55a and 55b are so formed that gases are injected toward the beam incident point, as in FIG. 4B. The operator horizontally moves the overall gas supply mechanism by using a driving mechanism 53, such that the portion to be processed on the sample 48 is located below the center of the hole 54.
The nozzle type and cylinder type gas supply mechanisms have been described above.
Recently, as a mask for transferring an LSI pattern onto a wafer, phase shift masks which are improved in the resolution by using the phase shift effect are used as well as common chromium (Cr) masks. Among other phase shift masks, a Levenson type mask has a high resolution and is therefore considered to be essential in the fabrication of devices from 1-Gbit DRAMs. When such phase shift masks are used, no good pattern transfer can be performed if the shifter has defects, so it is necessary to completely correct defects.
In one method, if a defect exists in a Levenson mask phase shifter, this defect is corrected by irradiating a focused ion beam described above on the defect. In this method, however, the phase shifter and the mask substrate are constituted by the same element, so the end point of etching is difficult to detect. Also, it is very difficult to etch only a projecting defect, and, even if a projecting defect alone can be etched, the shape after the etching depends upon the shape of the projecting defect.
One possible method by which these problems can be solved is to cover a projecting defect with a deposition film so that the upper surface is planarized, and etch the deposition film containing the projecting defect with a focused ion beam under the conditions in which the projecting defect and the deposition film are etched at the same etching rate, thereby removing the projecting defect together with the deposition film.
In assisted deposition using a focused ion beam, however, depending on the type of deposition film it is difficult to cover a projecting defect so that the upper surface of the deposition film is planarized. That is, when the thickness of the deposition film is increased to a certain degree, the step of the deposition film in a portion covering the edges of a projecting defect decreases. However, this deposition film step is difficult to completely remove even if the film is deposited to have a larger thickness. As a consequence, when etching is performed from over the film with the step, the shape after the etching depends on the shape of the step, so the projecting defect is difficult to planarize or remove. In correction of a recessed defect, on the other hand, it is difficult to correct the defect such that the surface of the buried portion is level with the surface of the rest of the shifter.
As described above, the use of a focused ion beam in correction of a Levenson type masks has been conventionally studied. However, since it is difficult to planarize a defect with a deposition film, it is difficult to correct the defect so as to be level with the substrate surface.
To solve the above conventional problems, the present inventors have already proposed a structure defect correction method (Japanese Patent Application No. 5-274491) capable of correcting a projecting defect or a recessed defect so as to be even with the substrate surface. This method makes use of the following arrangement.
That is, the first method is a structure defect correction method of correcting a projecting defect produced in a structure in which a desired pattern is formed on a substrate, comprising the steps of forming, on the substrate, a first thin film made of a material different from the substrate, so that the film is formed around or close to the projecting defect, forming a second thin film on the projecting defect and on the first thin film to thereby planarize the upper surface, simultaneously removing the projecting defect and the thin films formed on and around the defect by using a charged particle beam, and removing the thin films remaining in the first removal step.
The second method (FIGS. 5A to 5G) is a structure defect correction method of correcting a recessed defect produced in a structure in which a desired pattern is formed on a substrate, comprising the steps of burying a burying material in the recessed defect and forming a portion projecting from the substrate surface, covering a region including the projecting portion with a planarizing film made of a material different from the substrate, thereby planarizing the upper surface, simultaneously removing the projecting portion and the surrounding planarizing film by using a charged particle beam, and removing the planarizing film remaining in the first removable step.
It is considered that the use of the defect correction methods as above can correct a projecting defect and a recessed defect so as to be almost flush with the substrate surface.
In FIGS. 5A to 5G, reference numeral 200 denotes an ion beam; 201, a substrate; 202, a recessed defect; 203, a nozzle; 204, a source gas; 206, a deposition film; 207, a first deposition film; 208, a second deposition film; and 209, an etching assist gas.
Note that when the above correction methods are applied to a conventional focused ion beam apparatus, the amount of gas supply to the irradiation position of an ion beam is controlled by taking account of the acceleration voltage of the ion beam, current density, beam retention, and scanning time.
Unfortunately, even in correcting a recessed defect of a mask by deposition by using the defect correction methods described above, it is not easy to constantly deposit a thin film with a stable transmittance. In particular, it is still difficult to constantly deposit an SiO.sub.2 film with a high transmittance which is required for correction of a recessed defect. On the other hand, even if the above defect correction methods are used to correct a projecting defect of a mask by etching, it is difficult to correct the projecting defect so as to be well level with the mask surface. Also, similar problems arise when a thin film is deposited on the surface of a sample or when the surface of a sample is etched in regular mask processing, as well as in correction of defects of a mask.
Note that these problems occur regardless of whether the nozzle type or the cylinder type gas supply mechanism is used in a charged beam apparatus.
Accordingly, a demand has arisen for a charged beam apparatus capable of forming a thin film with a stable transmittance during deposition done by a focused ion beam apparatus or capable of well planarizing the mask surface during etching done by a focused ion beam apparatus.